Field of the invention
Embodiments of the invention generally relate to methods for determining the erosional characteristics of a mudcake in the presence of a washing/cleaning/spacer fluid (hereinafter collectively referred to as a “cleaning fluid”). More specifically, various embodiments of the invention relate to methods for measuring the efficiency of a cleaning fluid for removing the mudcake from a wellbore wall prior to well completion. In particular, some embodiments of the invention relate to methods for determining the ease of removing the mudcake from a wellbore wall by hydrodynamic action in the presence of a native fluid. Other embodiments of the invention relate to methods for determining the ease of removing the mudcake by the combined action of hydrodynamic forces and chemical interactions generated by a foreign fluid on the mudcake. Additionally, some embodiments of the invention relate to methods for determining a minimum soaking or interaction time required for the cleaning fluid to maximize the amount of the mudcake removed from the borehole or wellbore wall (hereinafter collectively referred to as a “wellbore wall”) prior to well completion.
Description of the Related Art
Horizontally/multilaterally-drilled wells have been used to enhance both hydrocarbon recovery and total well productivity from many types of reservoirs. Drilling, workover, and production operations may result in near-wellbore formation damage that in most cases cannot be prevented (e.g., pore plugging by calcium carbonate particles from drilling fluid, drilled solid particles, or particles from the formation).
During well operations, drilling fluids can be lost into the surrounding formation. To prevent this, the drilling fluid is frequently modified such that a small amount of the fluid and solids contained therein form a coating on a wellbore surface (i.e., the formation of a “filter cake” or “mudcake”—hereinafter referred to as a “mudcake”). After the completion of drilling operations, the mudcake is typically removed, and production from the formation can proceed. The process used to remove the mudcake can also be used to remove other types of damage or debris from the wellbore prior to beginning hydrocarbon production.
Effective removal of the mudcake prior to completing a well is very important for production of a well in commercial rate. Mudcake removal, though important for all wells, is very important for horizontal wells with barefoot completions. Failure of some horizontal wells to produce in commercial rates are related to plugging of the sand screens by the leftover mudcake materials and/or creation of a strong flow barrier at the cement-wellbore interface. The presence of some mudcake material on the wellbore wall dramatically reduces oil flow caused by the extremely low permeability of the mudcake. Typically, mudcake permeability ranges from 0.005 to 0.0012 mD (millidarcy). Hence, inadequate cleaning of the mudcake from the wellbore wall will create a highly detrimental effect on the productivity of a well.
Currently, there are no available, well-defined quantitative methods or API method for evaluating an ablation modulus of a mudcake in the presence of a native or foreign fluid. A reliable, well-defined, but simple, quantitative and statistically valid test facility and laboratory method, therefore, is needed for adequately evaluating the ablation modulus of a mudcake in the presence of a native or foreign fluid to determine the mudcake removal efficiency of various cleaning fluids.